/*
* Copyright (c) 2017 Thomas Pornin
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include "inner.h"
/*
* This file contains some additional functions for "i15" big integers.
* These functions are needed to support ECDSA.
*/
/* see inner.h */
void
br_i15_rshift(uint16_t *x, int count)
{
size_t u, len;
unsigned r;
len = (x[0] + 15) >> 4;
if (len == 0) {
return;
}
r = x[1] >> count;
for (u = 2; u <= len; u ++) {
unsigned w;
w = x[u];
x[u - 1] = ((w << (15 - count)) | r) & 0x7FFF;
r = w >> count;
}
x[len] = r;
}
/* see inner.h */
uint32_t
br_i15_bit_length(uint16_t *x, size_t xlen)
{
uint32_t tw, twk;
tw = 0;
twk = 0;
while (xlen -- > 0) {
uint32_t w, c;
c = EQ(tw, 0);
w = x[xlen];
tw = MUX(c, w, tw);
twk = MUX(c, (uint32_t)xlen, twk);
}
return (twk << 4) + BIT_LENGTH(tw);
}
/* see inner.h */
void
br_i15_decode(uint16_t *x, const void *src, size_t len)
{
const unsigned char *buf;
size_t v;
uint32_t acc;
int acc_len;
buf = src;
v = 1;
acc = 0;
acc_len = 0;
while (len -- > 0) {
uint32_t b;
b = buf[len];
acc |= (b << acc_len);
acc_len += 8;
if (acc_len >= 15) {
x[v ++] = acc & 0x7FFF;
acc_len -= 15;
acc >>= 15;
}
}
if (acc_len != 0) {
x[v ++] = acc;
}
x[0] = br_i15_bit_length(x + 1, v - 1);
}
/* see inner.h */
void
br_i15_from_monty(uint16_t *x, const uint16_t *m, uint16_t m0i)
{
size_t len, u, v;
len = (m[0] + 15) >> 4;
for (u = 0; u < len; u ++) {
uint32_t f, cc;
f = MUL15(x[1], m0i) & 0x7FFF;
cc = 0;
for (v = 0; v < len; v ++) {
uint32_t z;
z = (uint32_t)x[v + 1] + MUL15(f, m[v + 1]) + cc;
cc = z >> 15;
if (v != 0) {
x[v] = z & 0x7FFF;
}
}
x[len] = cc;
}
/*
* We may have to do an extra subtraction, but only if the
* value in x[] is indeed greater than or equal to that of m[],
* which is why we must do two calls (first call computes the
* carry, second call performs the subtraction only if the carry
* is 0).
*/
br_i15_sub(x, m, NOT(br_i15_sub(x, m, 0)));
}